Low ripple gear pump/motor

ABSTRACT

A gear pump system comprises a gear pump having an inlet, an outlet, and at least one rotating gear for pumping fluid from the inlet to the outlet and producing an output flow characterized by pressure pulses arising from the geometry of the teeth of the gear; and at least one valve operative to vary the output flow in timed relation to the rotation of the gear for counteracting the pressure pulses, thereby to reduce the amplitude of the pressure pulses.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/726,568 filed Oct. 14, 2005, which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention herein described relates to a low ripple gear pump/motor system and method, and more generally to an apparatus and method for reducing if not eliminating ripple from a fluid circuit.

BACKGROUND

Many gear pumps (and motors), because of the geometry of the gear teeth, inherently produce a small flow pulse for each gear tooth as the gears rotate, and this in turn produces pressure pulses. Such flow/pressure pulses are commonly referred to as ripple. The ripple can produce undesirable noise and vibration. The noise and/or vibration can become excessive if the ripple excites hydraulic resonance in the hydraulic system.

Increasing the number of gear teeth decreases flow ripple amplitude, but this technique has limitations. Three alternative technologies that are used today for low noise hydraulic gear pumps are known as Dual Flank Contact, Split Gear, and Helical Gear.

The Dual Flank Contact (DFC) design achieves low flow ripple by removing the backlash found in normal spur gears that provide single line contact. Zero backlash allows two-line contact thus increasing the frequency of pulsations while lowering the amplitude of the pulse.

The Split Gear design achieves the same result as DFC, but this is achieved by timing a sliding set of gears onto an integral set of gears that are phased by one half tooth pitch. The two gear sets are separated by a wear plate, which allows them to function as two pumping elements.

The Helical Gear Pump design is similar to a spur gear pump, except that the gears are made with an indexing angle such that each tooth is phased one full tooth pitch from one face to the other. The flow pulsation is drastically reduced as the teeth mesh. A drawback is that compensation must be made for the axial separating forces that are generated. Consequently, helical gears are rarely used for high pressure applications.

SUMMARY OF THE INVENTION

The present invention addresses the problem of ripple in a fundamentally different manner. Instead of modifying the source of the ripple as was done in the past, the ripple is removed by acting on the output flow of the pump in timed relation to the source of the ripple. More particularly, the ripple arising from the variable volume output/input of the gears of a gear pump/motor is counteracted by at least one valve that operates in timed sequence with the rotation of the gears. Preferably, a fast acting valve is employed and digitally pulse width modulated to vary the pump output flow in timed relation to rotation of gear teeth. The valve timing may be effected by any suitable means, such as by using position, speed, and/or pressure sensors. For example, a position sensor (i.e. proximity sensor) can be coupled to a rotating component of the pump to provide an output indicative of the position of the gears and, in particular, the position of at least one tooth of at least one gear. A respective fast acting valve can be controlled or timed to introduce a secondary pulse of flow “phased” with a ripple pulse. The valve may be controlled by a sensor, i.e. to “signal” a pressure peak and also a speed, to control the continued response of the fast acting valve. The speed of the fast acting valve versus the rotational speed of the pump will determine the “smoothness” of any remaining ripple.

As will be appreciated, principles of the invention can be applied to virtually any pulsating flow source and thus has potential for retrofitting known pump designs that exhibit the ripple phenomena. Moreover, this can be effected in a relatively inexpensive and simple manner. In addition, principles of the invention can be applied to hydraulic gear motors to reduce torque ripple at the output of the motor.

Accordingly, the invention provides a gear pump system comprises a gear pump having an inlet, an outlet, and at least one rotating gear for pumping fluid from the inlet to the outlet and producing an output flow characterized by pressure pulses arising from the geometry of the teeth of the gear; and at least one valve operative to vary the output flow in timed relation to the rotation of the gear for counteracting the pressure pulses, thereby to reduce the amplitude of the pressure pulses.

More particularly, the valve may be operative to introduce secondary pulses of flow in timed relation to the pressure pulses to counteract the pressure pulses. The valve, for example, may be a pulse width modulated valve. A sensor may be provided for producing an output synchronous with the pressure pulses, and a controller may control the at least one valve to introduce into the flow passage secondary pulses of flow “phased” with the pressure pulses.

The sensor may include a position sensor operatively coupled to the gears to provide a position output signal representative of the position of the gears, and/or a pressure sensor for sensing the pressure at the outlet of the pump.

According to a more general aspect of the invention, a system for counteracting pressure pulses in a fluid circuit comprises a fluid circuit characterized by pressure pulses, and a flow control device for varying the flow in the fluid circuit in a manner that counteracts the pressure pulses, thereby to reduce the amplitude of the pressure pulses. The flow control device may include at least one valve operative to open and close in timed relation to the pressure pulses for controlling flow of fluid to or from the fluid circuit. The valve may be operative under the control of the controller to introduce into the fluid circuit secondary pulses of flow “phased” with the pressure pulses.

According to still another aspect of the invention, a method for counteracting pressure pulses in a fluid circuit comprises the steps of using a sensor to provide an output synchronous with the pressure pulses, and operating a valve to vary the flow in the fluid circuit a function of the output of the sensor so as to vary the flow in fluid circuit in a manner that counteracts the pressure pulses, thereby to reduce the amplitude of the pressure pulses.

According to a further aspect of the invention, a motor system and method are characterized by a hydraulic gear motor having an inlet for receiving an input flow of pressurized fluid, an outlet, and at least one rotating gear rotated by flow of fluid from the inlet to the outlet and producing an output torque characterized by torque pulses arising from the geometry of the teeth of the gear; and at least one valve operative to vary the input flow pressure in timed relation to the rotation of the gear for counteracting the torque pulses, thereby to reduce the amplitude of the torque pulses.

Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings,

FIG. 1 is a diagrammatic illustration of an exemplary pump system according to the invention;

FIG. 2 is a diagrammatic illustration of another exemplary embodiment of a pump system according to the invention; and

FIG. 3 is a graphic illustration of pump ripple with and without the ripple smoothing effected by the present invention.

DETAILED DESCRIPTION

Referring now in detail to the drawings and initially to FIG. 1, an exemplary hydraulic gear pump system according to the invention is diagrammatically illustrated and designation by reference numeral 10. The system 10 comprises a gear pump 12 having an inlet 14, an outlet 16, and one or more rotating gears 18 for pumping fluid from the inlet to the outlet. As is known in the art, the output flow of the gear pump typically exhibits pressure pulses arising from the geometry of the teeth of the gear. In accordance with the invention, the pressure pulses, i.e. ripples, are “smoothed” by a ripple smoothing device 20 such that the amplitude of the pressure pulses passing downstream to a load 22 will be reduced, possibly to essentially zero thereby eliminating the ripple.

The ripple smoothing device 20 includes at least one valve 26 operative to vary the output flow in timed relation to the rotation of the gear or gears 18 for counteracting the pressure pulses, thereby to reduce the amplitude of the pressure pulses. The valve or valves are operatively connected to a rotating component of the gear pump by a phasing device 28. The phasing device 28 can take a variety of forms. For example, the phasing device may be a mechanical coupling, for example a train of gears and/or timing belt, between each valve 26 and a rotating component of the gear pump, such as one of the gear shafts 32. This will mechanically effect a timing relationship between the valve and rotational motion of the gears 18. As may be needed, the phasing device may include any suitable means for varying the phase between each valve 26 and the gears, as may be desired to optimize counteracting of the pressure pulses.

Counteraction of the pressure pulses is effected by operating each valve 26 so as to introduce secondary pulses of flow in timed relation to the pressure pulses to counteract the pressure pulses and/or partially dump fluid pressure in timed sequence with the pressure pulses. In the former case, the valve may be connected to any suitable source of pressure higher than the pressure at which the valve supplies the secondary pulses to the output flow of the pump. Such source of pressure, for example, may be provided by providing a flow restriction between the pump outlet 16 and the connection of the valve outlet to the outlet line 40 of the system.

Referring now to FIG. 2, another gear pump system 44 according to the invention is illustrated, this system including in particular electronic timing of the valve or valves 26. Here the phasing device includes a sensor 46 for providing an output synchronous with the pressure pulses, and a controller 48 for controlling the at least one valve to introduce into the flow passage secondary pulses of flow “phased” with the pressure pulses. The sensor, for example, may be a position sensor operatively coupled to the gears to provide a position output signal representative of the position of the gears 18. Alternatively or additionally, the sensor may be a speed or pressure sensor.

The valve 26 may be of any suitable type, such as a pulse width modulated valve. The controller 48 can control the modulation of the valve in timed relation to the position output of the position sensor. The valve preferably is a fast acting valve. At the vary least, the valve utilized should be capable of modulating flow at a rate at least equal the rate of pressure pulses at the maximum rated speed of the pump.

Referring now to FIG. 3, line 50 illustrates the pressure pulses produced by a gear pump whereas line 52 illustrates the amplitude attenuation resulting from the timed operation of the valve or valves 26 as above described. In actuality the plots will typically vary from what is shown in FIG. 3, but FIG. 3 is illustrative of the effect the invention may have in reducing the amplitude of the pressure pulses.

Although the invention has been described primarily in relation to a hydraulic pump, it will be appreciated that principles of the invention can be applied to virtually any pulsating flow source and thus has potential for retrofitting known pump designs that exhibit the ripple phenomena. Moreover, this can be effected in a relatively inexpensive and simple manner as above described.

In addition, principles of the invention can be applied to hydraulic gear motors to reduce torque ripple at the output of the motor. Such a system would be essentially the same as illustrated in FIG. 1, but with the load being a source of pressurized hydraulic fluid. A gear motor would typically exhibit torque pulsations because of the gear teeth geometry. The valve or valves would be operative to vary the input flow pressure in timed relation to the rotation of the gear for counteracting the torque pulses, thereby to reduce the amplitude of the torque pulses.

Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application. 

1. A gear pump system comprising a gear pump having an inlet, an outlet, and at least one rotating gear for pumping fluid from the inlet to the outlet and producing an output flow characterized by pressure pulses arising from the geometry of the teeth of the gear; and at least one valve operative to vary the output flow in timed relation to the rotation of the gear for counteracting the pressure pulses, thereby to reduce the amplitude of the pressure pulses.
 2. A system as set forth in claim 1, wherein the valve is operative to introduce secondary pulses of flow in timed relation to the pressure pulses to counteract the pressure pulses.
 3. A system as set forth in claim 1, wherein the valve includes a pulse width modulated valve.
 4. A system as set forth in claim 1, comprising a sensor for providing an output synchronous with the pressure pulses, and a controller for controlling the at least one valve to introduce into the flow passage secondary pulses of flow “phased” with the pressure pulses.
 5. A system as set forth in claim 1, wherein the sensor includes a position sensor operatively coupled to the at least one rotating gear to provide a position output signal representative of the position of the at least one gear.
 6. A system as set forth in claim 4, wherein the valve is a pulse width modulated valve, and the controller controls the modulation of the valve in timed relation to the position output of the position sensor.
 7. A system as set forth in claim 4, wherein the sensor includes a pressure sensor for sensing the pressure at the outlet of the pump.
 8. A system as set forth in claim 1, wherein the at least one valve is operated to modulate flow at a rate at least equal the rate of pressure pulses.
 9. A system for counteracting pressure pulses in a fluid circuit comprising a fluid circuit characterized by pressure pulses, and a flow control device for varying the flow in the fluid circuit in a manner that counteracts the pressure pulses, thereby to reduce the amplitude of the pressure pulses.
 10. A system as set forth in claim 9, wherein the flow control device includes at least one valve operative to open and close in timed relation to the pressure pulses for controlling flow of fluid to or from the fluid circuit.
 11. A system as set forth in claim 10, wherein the valve is operative under the control of the controller to introduce into the fluid circuit secondary pulses of flow “phased” with the pressure pulses.
 12. A system as set forth in claim 10, wherein the valve includes a pulse width modulated valve.
 13. A system as set forth in claim 10, wherein the fluid circuit includes a pump, and the pressure pulses are produced by the pumping action of the pump.
 14. A system as set forth in claim 13, wherein the at least one valve is mechanically connected to a rotating component of the pump.
 15. A system as set forth in claim 13, wherein the timing of the at least one valve is electronically controlled.
 16. A method for counteracting pressure pulses in a fluid circuit comprising the steps of using a sensor to provide an output synchronous with the pressure pulses, and operating a valve to vary the flow in the fluid circuit a function of the output of the sensor so as to vary the flow in fluid circuit in a manner that counteracts the pressure pulses, thereby to reduce the amplitude of the pressure pulses.
 17. A motor system comprising a hydraulic gear motor having an inlet for receiving an input flow of pressurized fluid, an outlet, and at least one rotating gear rotated by flow of fluid from the inlet to the outlet and producing an output torque characterized by torque pulses arising from the geometry of the teeth of the gear; and at least one valve operative to vary the input flow pressure in timed relation to the rotation of the gear for counteracting the torque pulses, thereby to reduce the amplitude of the torque pulses. 